joint disease

Several other types of polyarthritis resemble rheumatoid arthritis but characteristically lack the rheumatoid factors in the bloodstream. Psoriatic arthritis, associated with the skin disease psoriasis, differs from rheumatoid arthritis insofar as it has a predilection for the outer rather than the inner joints of the fingers and toes; furthermore, it results in more destruction of bone....

spondyloarthropathies

...plaques can occur on any surface of the body. About 10 percent of people with psoriasis (possibly as many as 30 percent in some regions of the world) develop a specific type of arthritis known as
psoriatic arthritis.